In the book to which I have referred, I also endeavoured to show that a knowledge of even elementary astronomy may be of very great assistance to students of archæology, history, folk-lore and all that learning which deals with man’s first attempts to grasp the meaning and phenomena of the universe in which he found himself before any scientific methods were available to him; before he had any idea of the origins or the conditionings of the things around him. [Illustration: FIG. 1.--Present sun worship in Japan.] It may be well, however, in the present book to restate the underlying astronomical principles in the briefest possible manner; and this is the more easily done because, in the absence of measuring instruments, the horizon was the only circle which the ancient peoples could employ effectively, and we need only therefore consider it. Indeed, whether we regard the Rig-Veda or the Egyptian monuments from an astronomical point of view, we are struck by the fact that the early worship and all the early observations related to the horizon. This was true not only for the sun, but for all the stars which studded the general expanse of sky. [Illustration: FIG. 2.--The celestial sphere, conditions at the North Pole. A parallel sphere. _N.P._, North celestial Pole; _N_, position of observer.] We have therefore chiefly to consider the relation of the horizon of any place to the apparent movements of celestial bodies at that place. [Illustration: FIG. 3.--The celestial sphere, conditions at the Equator. A right sphere. _Q_, standpoint of observer; _PP_, the celestial poles; _EW_, east and west points.] [Illustration: FIG. 4.--The celestial sphere, conditions in a middle latitude. An oblique sphere. In this woodcut _DD′_ shows the apparent path of a circumpolar star; _BB′B″_ the path and rising and setting points of an equatorial star; _CC′C″_ and _AA′A″_, those of stars of mid declination, one north and the other south; _O_, standpoint of observer.] We now know that the earth rotates on its axis, but this idea was of course quite unknown to these early peoples. Since the earth rotates, with stars infinitely removed surrounding it on all sides, the apparent movements of the stars will depend very much upon the position we happen to occupy on the earth. An observer at the North Pole of the earth, for instance, would see the stars moving round in circles parallel to the horizon (Fig. 2). No star could therefore either rise or set--one half of the heavens would be always visible above his horizon, and the other half invisible. An observer at the South Pole would of course see that half of the stars invisible to the observer at the northern one.